Patent GB-302231-A (GB)
Title: Improvements in power actuators
IPC: B60T13/24
Filed: 1928-12-03
Abstract: 302,231. Bragg, C. S., and Kliesrath, V. W. Dec. 12, 19'27, [Convention date]. Fluid-pressure.-Valve mechanism for a fluid - pressure actuated servo-motor, particularly for operating the brakes of motor vehicles, comprises a low pressure valve seated by a spring or other yielding resistance means, against the action of the difference of pressure of the lowpressure source and that in the cylinder of the servo-motor whereby the resistance felt by the operator in opening the valve indicates the pressure applied to the brakes &c., one face of this valve providing the seat of the higher pressure valve and a recess in the seat being in communication with the high pressure source. As shown in Fig. 1, the cylinder 101 of the servo-motor is normally open to, atmosphere and is connected to the induction pipe 163 of the engine of the motor vehicle to effect application of the brakes 176 of the vehicle to which the piston 103 is connected by link 178 and shaft 176. The valve casing 110 which is connected to the shaft 176 by rods 107, 183 provides the seating for the low-pressure valve 114 slidably mounted on the tubular stem 124 which passes freely through the valve casing and is secured to the high-pressure valve 116. The stem 124 is connected to the pedal 181 and is provided with an air inlet 120<b> to which an air-strainer 123 may be attached. The stem 124 has an aperture 122 opening into a chamber between the two valves. The valvechamber 111<a> communicates by pipe 126 with the suction pipe 163 of the engine and the chamber 111 by passage 107<a> and pipe 113 with the cylinder 101. The valve 114 which is thus subject to the opposing pressures of that in the suction pipe and the cylinder is held seated by a spring 115 which just counterbalances the maximum pressure difference existing when the brakes are released. In these conditions the valve 116 is unseated by the springs 182, 125 so that the cylinder 101 is open to atmosphere by way of chambers 111, 117 and stem 124. To apply the brakes the pedal is depressed so as first to seat the valve 116 on the valve 114 and then to unseat the valve 114. As the air is withdrawn from the cylinder 101 the pressure difference acting on the valve 114 to which is added that on the valve 116 decreases and the resistance felt by the operator in holding the valve open increases. The valve casing 120 being connected to the shaft 176 follows up the valves as the brakes are applied and if the pedal is held in an intermediate position the valve 114 becomes seated with the brakes partially applied, the operator being then relieved of the pressure of the spring 115. The operator may apply a direct effort to the brakes by engaging the valve 114 with a washer 110<d> on the valve casing. 'According to Fig. 5, the valve casing 310 is mounted directly upon the piston 303, the valve operated stem 324 being connected by a lever 380<b>, to a rod slidable in the piston rod and connected to the pedal at 380<a>. The valve casing is open to the interior of the cylinder by passage 308<a>. An arrangement is also shown in which the valve casing is mounted directly upon an extension of the piston rod passing through the closed end of the cylinder. ' A pipe connection 131, Fig. 1, may be provided for connecting the cylinder to other cylinders acting upon the same or other brakes.